I've created a new shop in Riften, on the lower docks. I can go to Riften and enter the store via the load door, and it takes me right inside. But when I go to leave, I go to the door and it says "To Riften" and I leave and the game crashes.
I'm wondering if you can only have load doors in the Tamriel cell, or in any cell?

The Riften docks are in the Tamriel worldspace, aren't they?

i'm having the same problem, as are a few other people it seems. its related to how much stuff you have in your building (i have a working save where even a single alteration causes the crash on leaving), and it only happens when leaving your modded cell for a city (exterior) cell. interior cell travel is fine. no solution or explaination has yet been found, and the more people it effects the more its starting to look like a genuine bug.